I'm in the same boat almost exactly (mine will be at about 72' but
that's close enough). The research I've done on this shows that the
common feed affects the patterns of all bands, but especially 10m.
This is because the 10m elements are effected by currents on the 20m
loop. If you seperate out the 10m feed (on a triband model) you
should do okay. (or seperate out all three for that matter) The 6m
kit that LB sells comes with a seperate balun and seperate feed line,
so you probably should follow this pattern as well.
I know that Cebik has a discussion on his pages about the quad common
feed situation. This is probably the best reference on this.
In a nutshell 20m performance according to NEC doesn't get effected
that much. 15m does a little but it's really, in the grand scheme of
things not too bad. 10m gain doesn't fall off much, but the sharp
pattern nulls go away and you are left with a pattern that is about a
180 degree circular "cartioid". (or Blob) LB's reasoning and
argument on this is that when 10m is open the effect of the pattern
isn't going to hurt you that much. Cebik does state that the
compromise of sharing the common feedline might be worth it to some
hams. It's really up to you. Match wise it works fine.
The situation does get worse when you add the WARC bands to the
antenna however. 12m wire also interacts with the 10m wire..
I'm probably going to go with the common feed on mine until the
Sunspots make 10m & 12m more viable. It certainly will be useable and
provide gain, but if 10m get's really hot, I'll probably put the
monoband yagi back up on a different tower, anyway.
That is if I ever get any of my towers up! :O(
Fred, W0FMS
On Wed, 23 Mar 2005 22:36:24 -0500, Bob T. <bobt@gloryroad.net> wrote:
> I'm ready to put a Lightning Bolt 2 element, 20/15/10m quad up at 80ft. I
> want to do this right the first time, and get the best reasonable performance
> from the antenna. Lightning Bolt supplies a 2:1 balun for a common feedpoint.
> The owner of the company sez this is the best way to feed the antenna for max
> performance, anyone who sez otherwise is wrong. But...he can't supply figures
> or pattern pics. Others favor the gamma match method, but still I haven't
> seen any concrete evidence that this is the best way. (believe me, I've
> scoured the web) Still others say a common feed point (feed line)is just no
> good; the only way to go is seperate feedlines for each band. Still no facts
> or figures to back up this claim. I am primarily concerned with maximum
> forward gain and a fairly good pattern. I won't quibble over .5-1.0 db or so.
> If it makes any difference, I am also interested in integrating a 3 element 6
> meter quad on the same boom. (seperate feed) and/or mounting a loaded 40 me
te
> r dipole along the boom of the quad. So, who has the facts? Please, no
> educated guesses or second hand anectdotes. Thanks.
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
> Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
> questions and ask for Sherman, W2FLA.
>
> _______________________________________________
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>
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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